Development of high temperature/oxidation- resistant PVD coatings for cutting tools using HIPIMS

A series of high temperature and oxidation resistant, nanoscale, multilayer PVD, hard coatings have been developed through combine DC Unbalanced Magnetron (UBM) and High Power Impulse Magnetron Sputtering (HIPIMS) deposition technologies. The properties of the coatings lend themselves to the application of protecting cutting tools exposed to harsh environment such as the dry, high-speed machining of abrasive materials. This thesis discusses the literature supporting the project and pays tribute to the development of coatings that formed the foundation for the CrAlYBCN/AlSiCN coating series. Plasma diagnostics optimised the process conditions for deposition; a highly ionised metal rich plasma was generated to investigate the effect of process conditions during the pretreatment step. It was found that metal ion implantation into the substrate was successful and that ramping the cathode charge had little effect of the sputter rate of the substrate. Ion etching removed loosely bound surface grain to improve adhesion. A series of coatings were developed that were deposited at different levels of target poisoning, in an attempt to improve coating properties by process control and stoichiometry. Superhard coatings able to withstand temperatures of over 800 °C were produced. The coatings were subjected to a series of mechanical and thermal testing using pin on disk, microhardness, scratch test, Rockwell indentation, isothermal heat treatment and thermogravimetric analysis. Mechanisms of wear and oxidation process have been proposed based on the evidence given. Through coating development two coatings were indicated as having the desired chemical, thermal and mechanical properties suitable for cutting tests. The coating that was deposited at higher bias improved the tool lifetime by 5 times.